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tortoise

tortoise (tôrˈtəs) [key], common name for a terrestrial turtle, especially one of the family Testudinidae. Tortoises inhabit warm regions of all continents except Australia. They have club-shaped feet with reduced toes adapted for walking on land, and nearly all have high-domed shells. The limbs are covered with hard scales and when the limbs and head are withdrawn into the shell, the animal is completely closed off.

The most famous tortoises are the giant tortoises of islands in the Indian Ocean ( Aldabrachelys gigantea ) and of the Galápagos Islands ( Chelonoidis nigra ). Galapagos tortoises may reach a length of over 4 ft (120 cm) and weigh over 500 lb (225 kg). There are about a dozen races of the Galapagos tortoise, most of them isolated on separate islands. These tortoises were a major source of meat for sailors in the 17th and 18th cent. and were often slaughtered wantonly. Once so abundant that the islands were named for them ( galápago is Spanish for tortoise), they became extinct on some islands and were endangered on most of the others. The tortoises are now protected by law, and scientists from the Charles Darwin Research Station have bred some 2,000 and set free the different subspecies on the islands from which they came.

North American tortoises, genus Gopherus, are burrowing forms with flattened feet and heavy nails. Three of the four species are very similar. The desert tortoise, Gopherus agassizii, inhabits deserts from S Nevada to NW Mexico; the Texas tortoise, G. berlandieri, lives in arid brush country and open woods from S Texas to NE Mexico; the gopher tortoise, G. polyphemus, is found in high, sandy areas of Florida and the U.S. Gulf and Atlantic coasts. The desert and gopher tortoises reach a length of 13 in. (33 cm), while the Texas tortoise is about 81/2 in. (21.6 cm) long. The Bolson, or Mexican giant, tortoise, G. flavomarginatus, is a large species of NW Mexico. It has been much used for food, and the survival of the species is threatened.

Tortoises are extremely long-lived; there are authenticated cases of individuals living over 150 years. They are classified in the phylum Chordata, subphylum Vertebrata, class Reptilia, order Chelonia, family Testudinidae.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.

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